Not hard to keep if kept properly. Seems like you've done a bit of research, they are not photosynthetic, and require frequent almost nightly feedings to survive. It is best if every polyp recieves food but not necessary of fed enough. Each polyp can only take in and process so much food at once probably not much more than the polyp itself needs to be healthy, but feeding a majority of polyps will sustain unfed polyps. Problem is in maintaining good water quality with all the feeding, and keeping up with the feeding schedule after a long period of doing it it can become a bit of a chore that many people just dont keep up with.